Exhaust nozzle



Aug. 14, 1962 M. c. BENEDICT EXHAUST NOZZLE 2 Sheets-Sheet 1 Filed Oct. 29, 1959 ATTORNEY Aug. 14, 1962 M. c. BENEDICT 3,048,973

EXHAUST NOZZLE Filed Oct. 29, 1959 2 Sheets-Sheet 2 INVENTOR.

Marcus C33 en a di eTL ug/z,

ATTORNEY States atent fifice 3,048,973 EXHAUST NOZZLE Marcus C. Benedict, Glastonbury, Conn., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Oct. 29, 1959, Ser. No. 849,697 1 Claim. (1. Gil-35.6)

This invention relate to propelling nozzles for turbojet engines or the like and more particularly to a convergentdivergent type of propelling nozzle.

It is well known that the optimum in convergentdivergent nozzle performance over a wide range of operating conditions is obtained by utilizing a full multisegment convergent nozzle in combination with a full multisegment divergent nozzle both of which are capable of being simultaneously actuated and moved between a plurality of flow controlling positions. This type of propelling nozzle is, however, endowed with several inherent disadvantages. The first and foremost disadvantage resides in the fact that a nozzle of this type is extremely heavy and thus is objectionable from an aerodynamic standpoint. Another disadvantage stemming from this type of construction is the high initial cost. Closely related to cost is of course the factor of complexity of design. A full multi-segment convergent nozzle and a full multi-segment divergent nozzle are both comprised of a relatively large number of parts or components many of which are directly interconnected and coact with each other. Under operating conditions with the nozzles being exposed to high-temperature and corrosive exhaust gases, this complexity of design will obviously reduce the operational reliability of the nozzles.

In contrast to the aforementioned type of propelling nozzle, the present invention contemplates a convergentdivergent nozzle construction which employs a full-multisegment or variable diameter convergent nozzle in combination with a fixed diameter divergent nozzle. Excellent nozzle performance is achieved over a wide range of operating conditions by the introduction of external air into the fixed diameter divergent nozzle to supplement the secondary air flow or the airframe supplied air. in one specific embodiment of the invention this external air is introduced into the propelling nozzle in controlled quantities by a plurality of closures or blow-in doors carried by the engine shroud. The blow-in doors are actuated or moved between their flow controlling positions in response to changes in base pressure acting on the variable diameter convergent nozzle and are carried by the engine shroud to introduce the external air intermediate the variable diameter convergent nozzle and the fixed diameter divergent nozzle. From a comparative performance standpoint, a propelling nozzle constructed in accordance With the present invention will perform equally a well at maximum aircraft speeds as a full multisegment type of convergent-divergent nozzle and nearly or substantially as well at slower aircraft speeds.

Accordingly, one object of the present invention is to provide a convergent-divergent nozzle capable of optimum performance over a substantially wide range of operating conditions.

Another object of the invention is to reduce the weight, cost and complexity of a convergent-divergent nozzle.

Another object of the invention is to increase the base pressure and thereby reduce the base drag acting on a convergent-divergent propelling nozzle.

These and other objects of the present invention will become readily apparent to those skilled in the art from the following detailed description of a specific embodiment thereof taken in connection with the accompanying drawings, wherein:

FIG. 1 is a partial longitudinal section through a propelling nozzle embodying the present invention;

FIG. 2 i a schematic illustration of the propelling nozzle shown in FIG. 1 with the variable diameter convergent nozzle thereof assuming the fully retracted or open position;

FIG. 3 is another schematic illustration of the propelling nozzle shown in FIG. 1 with the variable diameter convergent nozzle thereof assuming the fully extended or closed position; and

FIG. 4 is a section taken along the line IV-lV of FIG. 1.

Referring more particularly to FIG. 1 of the drawings, there is shown and generally indicated by the reference numeral 18 a propelling nozzle of the convergent-divergent-type which is adapted to be carried or positioned on the exhaust end of a turbojet aircraft engine or the like (not shown). Propelling nozzle 11) includes an outer shroud or casing member 12, one end 14 of which defines an outlet for engine exhaust gases or products of combustion and the opposite end of which (not shown) is rigidly connected by any suitable means to the aircraft engine (not shown). in this particular embodiment of the invention, the shroud 12 is substantially cylindrical in configuration and may be made in any suitable size, the size of the shroud depending of course upon the size and type of engine with which it is to be used and the size of the components which is adapted to house or enclose.

A conduit means or exhaust duct 16 is carried within the shroud 12, and in this particular instance the exhaust duct 16 takes the form of an afterburner housing. One end 18 of the afterburner housing 16 defines an outlet for the engine exhaust gases and products of combustion and the opposite end thereof (not shown) is rigidly connected by any suitable means to the aircraft engine. The afterburner housing 16 is likewise substantially cylindrican in configuration in this embodiment of the invention and obviously may be made in any suitable size.

The flow of exhaust gases from the outlet end 18 of afterburner housing 16 is adapted to be controlled by a convergent nozzle mean or nozzle 2% the outlet end of which is capable of being varied in diameter. Convergent nozzle 20 includes a plurality of annularly arranged segments or flap members 22 (only two shown) which are slidably and rotatably supported intermediate the afterburner housing 16 and outer shroud 12 for movement substantially axially of the afterburner housing. Each flap member is also substantially arcuate or curvilinear in crosssection so that upon movement axially of the afterburner housing in opposite directions the ends of the flap members will define a nozzle outlet 24 which either progressively increases or decreases in diameter.

Each of the flap members 22 of convergent nozzle 20 is rotatably supported intermediate the afterburner housing 16 and shroud 12 by a plurality of rollers or bearings which are adapted to engage the inner and outer surfaces of each flap member. Two rollers 28 and 30 are shown in FIG. 1 in rotatable engagement with the inner surface of one of the flap members 22 and the rollers 28 and 30 are rotatably supported by a pair of brackets or the like 3-2 and 34, respectively, which in turn are secured or attached by an suitable means (not shown) to the outer peripheral surface of the afterburncr housing 16. Similarly, a roller 36 is shown in rotatable engagement with the outer surface of the flap member 22 and this roller is likewise rotatably supported by a bracket or the like 38 which is secured to the inner peripheral surface of the outer shroud 12. Inasmuch as the construction of several known types of variable diameter convergent exhaust nozzles is well known in the art and the construction of the variable diameter convergent exhaust nozzle 20 per se forms no part of the present in- J vention, further discussion thereof is deemed unnecessary.

The unit movement of the flap members 22 of convergent nozzle in opposite directions is preferably controlled by a plurality of fluid motors or actuators 40, only one of which is shown in FIG. 1. Each fluid motor includes a cylinder 42 in which is slideably disposed a piston 44 having a piston rod 46 connected thereto at one end thereof by a threaded connection. The opposite end of each piston rod 46 is pivotably connected at 48 to an upstanding ear or the like 50 on one of the flap members 22. Movement of each piston 44- is accomplished by admitting fluid under pressure into the cylinder 42 on one side or the other of the piston through a pair of conduits 52 and 54, one of the ends of which are connected to the cylinder 42 and the opposite ends of which are connected to a suitable fluid pressure source (not shown). The simultaneous admission of pressurized fluid into each cylinder 42 on one side or the other of the piston 44 therein Will produce the movement of pistons 44 in opposite directions which in turn will result in the movement in opposite directions of convergent nozzle 20. When the pistons 44 are moved to the right as shown in FIG. 1, the nozzle flap members 22 will also be moved or extended to the right and the size of the nozzle outlet 24 will of course be progressively decreased in diameter until the flap members reach their fully extended position, the fully extended position being determined mainly by the length of travel of the pistons 44. Conversely, when the pistons 44 are moved to the left as shown in FIG. 1, the nozzle flap members will also be moved to the left or retracted and the size of the nozzle outlet 24 will be progressively increased in diameter until the flap members reach their fully retracted position, this fully retracted position again being determined by the length of stroke or travel of pistons 44. It will also be noted that the cylinder 42 shown in FIG. 1 includes an ear or the like 56 on one end thereof by which the fluid motor 40 is pivotably attached at 58 to a bracket 60 carried on the inner periphery of the outer shroud 12. Bracket 60 may be secured to the shroud 12 by any suitable means (not shown).

Adjacent the outlet end 14 thereof, shroud 12 carries a fairing-type ejector means or ejector 62 which assumes the form and function of a fixed diameter divergent nozzle means or nozzle. The divergent nozzle 62 is a substantially one-piece construction and is attached to the inner periphery of the shroud 12 by any suitable means (not shown). The design characteristics of divergent nozzle 62 in any given or particular instance are critical, and nozzle 62 is accordingly provided with a fixed or predetermined throat diameter, a predetermined length and a predetermined exit diameter, the exit diameter in this specific embodiment of the invention substantially coinciding with the diameter of shroud outlet 14. These critical design characteristics will of course vary with the design characteristics of the engine with which the convergent nozzle is used and will be determined mainly by such factors as the velocity and temperature of the gases discharged by the nozzle, the pressure drops across the nozzle, the speed of the aircraft on which the nozzle is mounted, etc.

As best seen in FIGS. 1 and 4, shroud 12 is provided with a plurality of ports or inlets 64 therein (only four shown) for admitting external air into the fixed diameter divergent nozzle 62. Inlets 64 in this particular instance are annularly arranged about the periphery of shroud 12 and each inlet is substantially identical in size and substantially rectangular in cross-section or configuration. It will also be noted that air inlets 64 are positioned in shroud 12 adjacent-to or slightly upstream of the fixed diameter divergent nozzle 62 and being so positioned will permit the inlet flow of external air to flow over the outer peripheral surface of convergent nozzle 20 and directly into convergent nozzle 62, this inlet flow of ex- 4 ternal air and the function thereof is to be discussed more in detail hereinafter.

Means is also carried by the shroud 12 for opening and closing the inlets 64 to thereby control the admission of external air into divergent nozzle 64. In this particular embodiment of the invention, each inlet 64 is adapted to be opened and closed by a door or the like 66, hereinafter referred to as a blow-in door, which in operation is moved or rotated between a plurality of flow controlling positions relative to the inlet 64 in response to differential pressures acting thereon. Each blow-in door in this specific embodiment of the invention (FIG. 4) is pivotally connected at one edge thereof to the shroud 12 by a double-leaf hinge 68, one leaf 70 of which is rigidly connected to the blow-in door 66 and the other leaf 72 of which is rigidly connected to the shroud 12. The hinge leaves 70 and 72 are preferably connected to the blow-in door 66 and shroud 12, respectively, by a plurality of rivets or the like 74 although it will be appreciated that any other suitable type of securing or connecting means may be employed. A hinge pin 76 extends through or is carried in the strap members 78 of the hinge to retain the two leaves 70 and 72 in assembled engagement.

It will also be noted that the end of each blow-in" door opposite the hinge 68 or the downstream end of each blow-in door is recessed or angularly bent to provide a lip or ledge 80 thereon. When the blow-in doors are in the closed position as shown in FIGS. 1 and 4, the lip 80 affords a lap seam type of joint or connection between the downstream end of each blow-in door 66 and the shroud 12, and further serves as a stop means or means of limiting the rotary movement of each blowin door in one direction beyond a predetermined position. It Will also be appreciated that the lip 80 will permit each blow-in door 66 to fit smoothly or blend into the contour of the shroud 12 when the blow-in door is in the closed position.

The operation of the propelling nozzle of the present invention can best be explained by reference to FIGS. 2 and 3. Referring particularly to FIG. 2, let it be assumed that the aircraft (not shown) is flying or moving at a high Mach number speed with the engine afterburner in operation. At this high Mach number-afterburning operationthe divergent nozzle 20 will have been fully retracted or moved to its fully open position and the blow-in doors 66 will have been moved to their closed position to thus prevent the admission of external air into the divergent nozzle 62. There will, however, be a flow of secondary air S in the space or passage between the inner peripheral surface of shroud 12 and the outer peripheral surface of the afterburner housing 16. This secondary air S, in this particular instance, is supplied by ram scoops or the like (not shown), and flows in the direction indicated by the arrows along the outer and inner peripheries of convergent nozzle 20. This secondary air S has both an aerodynamic and a cooling function, and the aerodynamic function thereof is closely related to the operation of the blow-in doors 66, as will be explained more in detail immediately hereinafter. With the blow-in doors 66 closed as shown in FIG. 1 and with the convergent nozzle 20 fully retracted, the secondary air flow in combination with the divergent nozzle 62 will produce a divergent nozzle of optimum performance, i.e., a divergent nozzle having a length vs. diameter of throat ratio and diameter of exit vs. diameter of throat ratio which provides the highest exit velocity for a given flow condition.

To explain the aerodynamic function of secondary air S, again referring to FIG. 2, let it be assumed that the exhaust gases flowing from afterburner housing 16 will impinge on a small area of the inner peripheral surface of convergent nozzle 20 at the tip or outlet end 18 thereof and will exert a pressure P thereon. This pressure P will of course act normal to the tip area of the convergent nozzle 20 and this normal force can be resolved into components. One of the components of P when resolved will exert a drag force on the convergent nozzle 20 and will tend to retard or slow the speed of the aircraft. The secondary air S, on the other hand, flowing over the outer peripheral surface of convergent nozzle 20 will also impinge on a similar area near the tip of convergent nozzle 20 on the outer peripheral surface thereof and will exert a pressure P thereon or a pressure commonly called base pressure. This base pressure P can also be resolved into components and, when so resolved, one of the components thereof exerts a thrust force on the convergent nozzle 20, this thrust force tending to increase the speed of the aircraft. With P and P exerting drag and thrust forces, respectively, on the convergent nozzle 29, it thus becomes imperative that P be maintained as large or as high as possible in order to minimize or eliminate the resultant drag force or base drag acting on the convergent nozzle 20. The best or optimum aircraft performance is obtained when this base drag is minimized or completely eliminated.

The aerodynamic effect of the base pressure P as related to operation of the blow-in doors 66 can best be explained by reference to both FIGS. 2 and 3. In FIG. 2, with the aircraft moving at a high Mach number speed and with the afterburner in operation, P will be at a maximum and more important will be higher than the outside or ambient pressure P which acts on the outer peripheral surface of the blow-in doors 66. P being higher than P will create a differential pressure which when acting on these blow-in doors 66 will move or rotate the blow-in doors to the closed position. With P at a maximum and the secondary air flow S thus maintaining the base drag at a minimum, there is no need for the introduction of external air.

Referring now to FIG. 3, let it be assumed that the variable diameter convergent nozzle 20* has been moved to its fully extended or closed position with the aircraft moving at a slower speed and with the engine afterburner not in operation. The pressures P and P will now act on much larger surface areas of the convergent nozzle 20. More important, however, is the fact that P will now be lower than P due to the lower speed of the aircraft. With the base pressure P being reduced, P will of course exert a greater resultant drag force or base drag on convergent nozzle 20 which in turn will tend to reduce the speed of the aircraft. It thus becomes imperative to increase the base pressure P Since P is now greater than P the blow-in doors 66 will automatically be blown-in or opened by the differential pressure acting thereon and external or ambient air will be admitted through the ports 64, this external air flowing over convergent nozzle 20 and being discharged through divergent nozzle 62. This external air flowing over the convergent nozzle 20 will increase the base pressure P and in so doing will decrease the base drag.

The blow-in doors 66 in being moved from the closed position will always be blown-in to an equilibrium position determined by the pressure differential between P and P For every combination of convergent nozzle positions and engine operating conditions including after burning and non-afterburning operations, a different P to P gradient will be created which in turn will result in the blow-in doors assuming a plurality of flow controlling positions. If P is greater than P the blowin doors will be automatically opened and will assume a predetermined or equilibrium position wherein they will admit a controlled quantity of external air. The exact P, to P gradient will locate the predetermined or equilibrium position of the blown-in doors. If P, is less than P the blow-in doors will obviously be urge-d or retained in their closed position. While in this one specific embodiment of the invention the means for admitting external air into the propelling nozzle has taken the form of doors or the like actuated by a differential pressure acting thereon, it will be appreciated by those skilled in the art that doors or the like actuated by any other suitable means such as fluid motors or the like could also be successfully employed. Furthermore, it will be obvious that many modifications of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

A propelling nozzle for a jet engine or the like comprising a tubular shroud, an exhaust duct carried within said shroud and having an outlet end terminating within said shroud for conducting combusted gas therethrough, convergent nozzle means carried within said shroud and being movable between a plurality of flow controlling positions relative to the outlet end of said exhaust duct, said shroud and said convergent nozzle means defining between them a passageway for the admission of secondary air, ejector means carried within said shroud defining a divergent nozzle for the passage therethrough of gases from said convergent nozzle and air from said passageway, said ejector means having the form of a diverging nozzle fairing of predetermined length, throat diameter and exit diameter and being connected to said shroud means, said shroud means having a plurality of ciroumferentially arranged ports for admitting ambient air into said passageway, and closure means for closing said ports operable by the pressure differential between the secondary air and ambient air for admitting ambient air into said passageway when the pressure of said secondary air drops below a predetermined value, said closure means being separate doors arranged to cover said ports and hinged to said shroud at their forward end for opening inwardly of said shroud.

References Cited in the file of this patent UNITED STATES PATENTS 2,597,253 Melchior May 20, 1952 2,788,184 Michael Apr. 9, 1957 2,882,679 Karcher Apr. 21, 1959 2,910,829 Meyer Nov. 3, 1959 FOREIGN PATENTS 1,180,334 France Dec. 29, 1958 1,188,450 France Mar. 16, 1959 788,316 Great Britain Dec. 23, 1957 OTHER REFERENCES Pearson: Exhaust Nozzles for Supersonic Aircraft, Journal of the Royal Aeronautical Society, vol. 62, No. 573, September 1958, pages 658-662,- pages 661 and 662 relied on. 

